Magnetostrictive microphone



1943- Y. ROCARD I ,4

'MAGNETOSTRICTIVE MICROPHONE Filed Feb. 24, 1940 May 1 e fos fr/cf) i'c 4 INVENTOR YVELS -ROCARD- ATTORNEYS Patented Aug. 31, 1943 MAGNETOSTRICTIVE MICROPHONE Yves Rocard, Paris, France; vested in the Alien Property Custodian Application February 24, 1940, Serial No. 320,608 In France March 22, 1939 4 Claims. (Cl. 177-386) The present invention is for improvements in or relating to magnetic apparatus and particularly to magneto-striction microphones and has for its object the provision of means for attenuating the mechanical resonance in apparatus such as magneto-striction microphones. In apparatus in which the sonorous pressures .are transformed into variations of magnetic phase'in a coil, a mechanical resonance is desired in order to increase the sensitivity. It will be understood, for example, that if a microphone is designed to receive frequencies in the vicinity of 15,000 per second, if it be estimated that the head-phones and the ear only require after heterodyning, a passing band of 1500 cycles per second, a mechanical resonance on 15,000 with a band width of 1500, constitutes the ideal solution. Unfortunately experience indicates that with known systems the mechanical resonance, even dampened by radiation in water, is always too acute and the width of band of uniform response desired is not attained. By voluntarily creating a supplementary mechanical damping, this eifect can be attained but it is detrimental to the sensitivity.

This invention presents a novel means by which the passing band is increased without losses due to a supplementary damping. It is applicable in particular to apparatus in which a bar or a tube of magneto-strictive metal enters into longitudinal vibrations in the normal working of the apparatus and it consists of a terminal section of the bar or tube being cut at right angles in order to fix it on to a piston or a diaphragm, and of cutting obliquely the other section. so that the bar operates as a plurality of narrow bars placed side by side but of unequal length. A particularly efficient construction is obtained with a laminated bar, the plates of which are of unequal length. The extremity of the sheets regularly distributed in order to produce the oblique design may remain free or may be soldered to a mass placed obliquely or in a straight manner on the .bar. It is not necessary for the section to be fiat and any profile whatever can be given to it. Experience shows that, under these conditions, the microphone using the resonance of such a bar retains its entire sensitivity with a width of passing band increased by 50% to 100% according to circumstances, which effect is desired for listening to submarine noises. In test arrangements an inclination of 45 to 60 of the terminal section has 'given good results.

The invention will be more particularly de scribed with reference to the accompanying drawing in which:

Figures 1 and 2 illustrate two methods of carrying the invention into effect.

Referring to Figure 1 which illustrates in perspective the mounting of a laminated magnetostrictive bar I, all the magnetic circuits and accessories being removed. The bar I, cut obliquely according to the invention, is surmounted by the mass 2 represented as having the same height above each bar, which is in no way necessary. The bar I is soldered, on to the piston 3 of the diaphragm, the edge 4 of which is utilized in the fixture, while a coil 5 connected to a proper source of current surrounds the bar.

Figure 2 illustrates in perspective, a thin cylinder of magneto-strictive metal with its upper extremity cut obliquely and having the lower extremity thereof soldered to the piston 3, also having a coil 5 surrounding the same and having a diiierent form of diaphragm which'is intended for example to be held in a rubber mounting.

What- I claim as my invention and desire to secure by Letters Patent of the United States is:

1. In a magneto-striction apparatus such as a magneto-striction microphone having a diaphragm, the combination of a straight vibrating bar fixed to the said diaphragm at one of the extremities thereof so as to project longitudinally from the same along the axis thereof, the other extremity terminating in an oblique section.

2. In a, magneto-striction apparatus such as a magneto-striction microphone having a diaphragm, the combination of a vibrating bar in the form of a straight elongated member having inner and outer sides fixed to the said diaphragm at one of the extremities thereof so as to project longitudinally from the same along the axis thereof, the other extremity terminating in an oblique section so as to present an end portion out of parallel with respect to said diaphragm.

3. In a magneto-striction apparatus such as a magneto-striction microphone having 3. diaphragm, the combination of a vibrating bar subdivided into flat straight strips of progressively increased length in the direction of the length thereof and fixed to the said diaphragm at one of the extremities thereof so as to project longitudinally from the same along the axis thereof,

the other extremity terminating in an oblique YVES ROCARD. 

